Geologic Time. Middle and Recent Earth History. Before You Read. Read to Learn

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1 chapter 10 3 Geologic Time section 3 Middle and Recent Earth History What You ll Learn about Mesozoic and Cenozoic life-forms how plate tectonics affected organisms during the Mesozoic Era when humans first appeared Before You Read Think about a picture of a dinosaur you have seen. On the lines below, describe how dinosaurs are different from modern animals. Summarize As you read each paragraph, write one sentence that states the main idea. Use vocabulary words in your sentence, if possible. C Study Coach Compare and Contrast Make the following Foldable to record how the Mesozoic and Cenozoic Eras are similar and different. 148 Geologic Time Read to Learn The Mesozoic Era People have been interested in dinosaurs since their bones were first discovered more than 150 years ago. Dinosaurs lived during the Mesozoic (meh zuh ZOH ihk) Era. The Mesozoic Era, or era of middle life, occurred between 248 and 65 million years ago and was a time marked by rapid movement of Earth s plates. What changes occurred to Pangaea? At the beginning of the Mesozoic Era, all the continents were joined and formed one landmass called Pangaea. During a part of the Mesozoic Era called the Triassic Period, Pangaea began to break up. The continents began to drift apart as Earth s plates moved away from each other. Pangaea split in two. Over time, the continents we know today formed. Some species, such as reptiles, survived the tremendous changes and mass extinction that occurred at the end of the Paleozoic Era. In the early Mesozoic Era, the climate became drier. The reptile s scaly skin kept in moisture, so reptiles could live in this drier climate. Reptile eggs are protected by a shell, so their young survived as well. Reptiles became the most abundant animals of the Mesozoic Era.

2 What were the dinosaurs like? Dinosaurs came in all shapes and sizes. Some were less than 1 m tall. Others, like Apatosaurus and Tyrannosaurus, were enormous. The first small dinosaurs appeared in the Triassic Period. Larger dinosaur species evolved during the Jurassic and Cretaceous Periods. Throughout the Mesozoic Era, some dinosaurs became extinct as others evolved. Were dinosaurs active? Generally, the faster an animal runs, the farther apart its footprints are. Paleontologists have studied fossil footprints from dinosaurs. They have found that some dinosaur footprints were far apart, indicating that these species were fast runners. Scientists figured out that some dinosaurs could run up to 65 km/h as fast as a modern racehorse. Studies also indicate that some dinosaurs might have been warm-blooded animals, not cold-blooded like reptiles. What evidence shows this? The bones of warm-blooded animals don t have growth rings, like the bones of cold-blooded animals. Dinosaur bones don t have growth rings either. They are similar to mammal bones as shown in the figures below. 1. Explain How do scientists know that some dinosaurs were fast runners? Dinosaur bone Mammal bone These findings indicate that some dinosaurs were likely active warm-blooded, fast-running animals, similar to modern mammals and birds. In fact, dinosaurs may have been very different from present-day reptiles. Were dinosaurs good mothers? The fossil record shows that some dinosaur species fed and took care of their young. These dinosaurs also traveled in herds, so the young were protected. Maiasaura acted in this way. Maiasaura mothers gathered together to build nests in colonies. The mothers laid their eggs and, after the young hatched, fed and cared for their offspring. Scientists have found fossils of hatchlings and adult dinosaurs in the same nest. Maiasaura mothers may have fed and tended their young until they were old enough to leave the nest. Picture This 2. Describe How are the dinosaur bone and the mammal bone alike? Reading Essentials 149

3 What were the first bird-like creatures? Some paleontologists believe that modern birds evolved from small, meat-eating dinosaurs. The earliest bird-like dinosaur known, Archaeopteryx, had both wings and feathers. Since Archaeopteryx had some features different from modern birds, it is not a direct ancestor of today s birds. What were the first mammals like? The first mammals appeared in the Triassic Period. These tiny, mouselike animals were warm-blooded and covered with fur, as shown in the figure below. The females produced milk to feed their young. Because of their furry coat and milk production, mammals where able to survive many changing environments. Picture This 3. Describe How does the early mammal resemble modern mammals, like mice or shrews? 4. Compare How are gymnosperms and angiosperms alike? What are gymnosperms? Gymnosperms (JIHM nuh spurmz) first appeared during the Paleozoic Era. By the Mesozoic Era, gymnosperms dominated the land. Gymnosperms are plants that produce seeds in cones, like pine cones. They do not produce flowers. There are many species of gymnosperms on Earth today, including pine trees and ginkgo trees. What are angiosperms? Angiosperms (AN jee uh spurmz) are flowering plants that evolved during the Cretaceous Period. Angiosperms produce seeds with hard outer coverings. Because their seeds are covered and protected, angiosperms can survive in many environments. Angiosperms are the most diverse and abundant plants on Earth today. Today s magnolia trees and oak trees first evolved during the Mesozoic Era. 150 Geologic Time

4 What ended the Mesozoic Era? The Mesozoic Era ended about 65 million years ago, when most land and ocean species became extinct. The dinosaurs disappeared. Many paleontologists hypothesize that this mass extinction was caused by an asteroid that collided with Earth. The impact put a huge cloud of dust and smoke in the air, blocking sunlight. Without sunlight, plants died. As a result, the animals that fed on plants died. Some organisms managed to survive. They are the ancestors of the many species on Earth today. The Cenozoic Era The Cenozoic (se nuh ZOH ihk) Era began about 65 million years ago and continues today. During this time, mountain ranges in North and South America formed. In the late Cenozoic, the climate cooled and ice ages occurred. The early Cenozoic Era is called the Tertiary Period. The present time is part of the Quaternary Period, which began about 1.8 million years ago. Which mountain ranges formed during this era? Many mountain ranges formed during the Cenozoic Era as Earth s plates moved and collided. These include the Alps in Europe and the Andes in South America. Many people think the growth of these mountains helped create cooler worldwide climates. How have mammals evolved? During the Cenozoic Era, grasslands expanded. As a result, grazing mammals like horses, deer, and elephants survived and grew larger. Horses evolved from small animals with many toes into the large, hoofed animals of today. Some mammals evolved to live in the sea, such as dolphins and whales. As the continents continued to move apart, some species became isolated. For this reason, animals like kangaroos and koalas evolved in Australia and are not found anywhere else on Earth. Modern humans, Homo sapiens, probably first appeared about 140,000 years ago. The appearance of early humans may have caused the extinction of many other mammals. Humans competed for food that other animals ate and also hunted animals. 5. Identify What geologic era are we living in today? 6. Identify What is the scientific name for the modern humans? Reading Essentials 151

5 After You Read Mini Glossary Cenozoic Era: geologic time that began about 65 million years ago and is continuing today Mesozoic Era: geologic time between about 248 and 65 million years ago, that was marked by rapid movement of Earth s plates and was when dinosaurs lived 1. Review the terms and their definitions in the Mini Glossary. Then write one sentence describing one of the eras. 2. Fill in the blanks in the boxes below by listing the plants, animals, and Earth changes for each era. MESOZOIC ERA Plants Changes in Earth Animals Plants CENOZOIC ERA Animals Changes in Earth 3. You summarized the main idea in each paragraph as you read this section. How did summarizing help you understand and remember the information in the text? End of Section 152 Geologic Time Visit blue.msscience.com to access your textbook, interactive games, and projects to help you learn more about the Mesozoic and Cenozoic eras.